ABSTRACT
In the last chapter, we discussed quasi-experimental designs and some of their weaknesses. Remember that quasi- and randomized experimental designs both have an active independent variable, but in randomized designs the participants are randomly assigned to the experimental and control groups. Random assignment of participants to groups should eliminate bias on all characteristics before the independent variable is introduced. This elimination of bias is one necessary condition for the results to provide convincing evidence that the independent variable caused differences between the groups on the dependent variable. For cause to be demonstrated, other biases in environmental and experience variables occurring during the study also must be eliminated.
